Just in case anyone is wondering, you can put 800lbs of weight on the back hatch without a spare tire and it will hold.
I needed to get some gravel for a wall I am building and got about 800 lbs. of gravel in bags at the local construction place. I do not carry my spare so there is nothing to hold up the spare tire cover but it did hold the weight just fine. It didn't even bow at all and I had a 5 mile drive home on some bumpy roads. I am impressed.